classic 150, etc versus Schneider Electric Charge controllers

More or less, Vmp-actual is based on temperature and a minimum amount of sun (say weak morning sun directly on panels). Once you have that minimum sun, the panels will be operating at Vmp-actual (i.e., temperature of cells, and to a degree, a slight variation of current draw).

https://forum.solar-electric.com/discussion/5458/two-strings-in-parallel-with-unequal-string-voltages

Here is one example curve from the above link:

Three different Watts per sq meter from 100% to 60% sun... See Vmax-power between those solar levels hardly changes...

Note there are two sets of curves here... One is simply current vs voltage at xxx W/m^2. The other set is Power (Watts) vs voltage--And that is the one we "care about".

An MPPT based controller is supposed to find that "peak power" point in the Power/Sun curve. Not all MPPT controllers are the same... Some work better than others. And some can "have issues" when clouds pass in front of sun, two or more arrays in parallel (i.e., one east facing, another west facing), random shading, etc...

More or less, once there is "enough sun" to produce a "useful amount of power (i.e., more than a few percent of output)--Then if you have YY panels in series, you will have YY*Vmp per panel of output voltage.

Just follow the MPPT input specs... I.e., Vmp-array-hot (minimum startup voltage) and Voc-array-cold. Whether that is a Vmp-array-std~36 Volts charging  a 12 volt battery bank, or a 200 to 600 Vmp-hot to Voc-cold array spec, it all will work fine...

Remember that in reality, there are a bunch of Vmp=0.5 volt cells in series--I.e., 36 cells in series for a Vmp=18volt... So whether you have 36 cells for 18 Volt Vmp or 360 cells in series for 180 Volt Vmp--There is no "issue" with high voltage input controllers and a bunch of panels in series--Other than the usual (min/max temperatures, no random shadows on panel(s) in array, "array" facing on one plane, etc.).

-Bill